Testing dissipative collapse models with a levitated micromagnet

We present experimental tests of dissipative extensions of spontaneous wave function collapse models based on a levitated micromagnet with ultralow dissipation. The spherical micromagnet, with a radius R = 27 mu m, is levitated by the Meissner effect in a lead trap at 4.2 K and its motion is detected by a superconducting quantum interference device. We perform accurate ringdown measurements on the vertical translational mode with frequency 57 Hz and infer the residual damping at vanishing pressure gamma/2 pi < 9 mu Hz. From this upper limit we derive improved bounds on the dissipative versions of the continuous spontaneous localization (CSL) and the Diosi-Penrose (DP) models with proper choices of the reference mass. In particular, dissipative models give rise to an intrinsic damping of an isolated system with the effect parametrized by a temperature constant; the dissipative CSL model with temperatures below 1 nK is ruled out, while the dissipative DP model is excluded for temperatures below 10(-13) K. Furthermore, we present the bounds on dissipative effects in a more recent model, which relates the wave function collapse to fluctuations of a generalized complex-valued space-time metric.